This invention relates to machine vision and, more particularly, to methods and apparatus for high accuracy machine vision searching
Searching is a fundamental operation in machine vision. It is used to determine the location of a mark, object or other "template" in an image. For example, in an industrial assembly operation, machine vision may be employed to determine the position of a part base on the position of an imprinted logo. To this end, an image of the part (i.e., the candidate image) is analyzed to find an image of the mark (i.e., the template image). Once identified, that location is passed to the assembly equipment for placement of the part.
The art suggest many searching schemes. Typically, these apply a correlation, or other matching, function to the template and portions of the candidate images, thereby, determining the location at which the candidate is most similar to the template. In some schemes, this function is applied at all locations in the candidate image. In others, it is applied at fewer, selected locations to reduce runtime processing. In either case, a final estimate of location can be made by interpolating between locations at which their is the greatest degree of similarity.
Such prior art schemes typically provide a resolution of .+-.0.1 pixels to .+-.0.5 pixels and, on average, of .+-.0.25 pixels. While this has traditionally proven quite acceptable, there is an increasing need for high accuracy searching.
An object of this invention, therefore, is to provide improved methods and apparatus for machine vision and, particularly, for high accuracy machine vision searching. A further object is to provide such methods and apparatus which can be readily adapted for use in a range of environments, which run rapidly with little runtime processing overhead.